Hardening alloying elements are widely used in powder metallurgy to produce high performance steel parts. These hardening alloying elements include: nickel, molybdenum and copper. One of the disadvantages of these alloying elements is their high and often fluctuating costs.
In traditional wrought steel metallurgy, additional hardening alloying elements comprise manganese, chromium and silicon. Manganese is a particularly effective hardening alloy. These additional alloying elements are less expensive and their costs tend to be more stable. The main disadvantage of these less expensive elements is that they are prone to oxidation which has, until now, limited their use in powder metallurgy.
There are a number of ways to introduce alloying elements in a powder metallurgy component. One of the ways involves adding alloying elements in the liquid steel before atomization (pre-alloying). Another way is to add the alloying elements to the powder mix as an additive (admixed). Pre-alloyed powders exhibit a relatively lower compressibility but produce more homogenous microstructures/properties. On the other hand, admixed alloying elements hinder the compressibility less but require higher sintering temperatures to ensure atomic diffusion, thus homogenous microstructures/properties.
GB 1,504,547 by Zaft et al, assigned to the company Sintermetallwerk Krebsöge GmbH, teaches a sintered alloy steel made by pressing and sintering a powder mixture with steel powder and a complex carbide hardening ferro-alloy containing the following elements: Cr up to 25%, Mo up to 25%, Mn up to 25%, C up to 10% as complex carbides and balance Fe. This exclusively containing carbide hardening ferro-alloy of Zaft et al., is very hard and can cause wear in the equipment and tools used in the production of steel parts (“Process for making alloyed steel sintered parts and sinter powder for use in the process” by G. Zapf et al., Patent GB 1,504,547, 1974). The conclusion that the master alloy of Zaft et al, causes excessive tool wear in processing equipment is explained in “New Cr—Mn-alloyed sintered steel for high-performance applications” by Paul Beiss, Advances in Powder Metallurgy & Particulate Materials, Part 7, Page 24, 2005.
Therefore, there is a need for a softer or less-hard master alloy for the production of hardened alloy steel parts, that reduces the use of costly hardening alloying elements and minimizes tool wear during production of these parts with a resulting saving in material as well as in production costs. It therefore makes the process viable. This master alloy should also protect from oxidation the oxygen-affinitive elements such as manganese and chromium during processing.